- The ice stored energy.

That is so cool to me!

Okay, it is, but that's a little too excited.

(chuckles) Pull it back.

How do you figure out how old a moon is?

You could look at the composition of its rock samples or look at radioactive decay, (chill lo-fi music) or you could look at its ice.

That's one way we've studied the faraway moons around Saturn.

And you can't just, like, pop by and pick up a sample too easy.

Remember when we talked about ice and all of its different crystal forms a couple months ago, and I mentioned that maybe amorphous ice deserved its own video?

This is it.

This is that video.

We're talking ice moons, electron microscopy, and what it all might have in common with a cocktail shaker.

(bell dinging) That one, that one back there.

Amorphous ice is ice that's amorphous.

Obviously.

The typical crystalline ice that we have down here on Earth has a defined ordered structure, but amorphous ice doesn't have that same kind of clear, long-range order.

If you imagine liquid water molecules moving around each other with some nearby attraction but no long-range order and then you just froze that in time, that's kind of what amorphous ice looks like.

In fact, it's sometimes even referred to as "amorphous solid water", which is descriptive but maybe a little silly.

Because amorphous ice doesn't have a repeating crystal structure, it's sometimes categorized as a glass.

And we've talked about glasses before that aren't the typical window glass that we think of, specifically in our Pop Rocks episode when we talked about sugar glass.

A glass is formed when you cool a molten material rapidly, locking its liquid structure in place.

This material could be sugar, in the case of Pop Rocks, sand or silica, in the case of window glass, or water, in the case of amorphous ice.

But amorphous ice is a little weirder than normal glass.

A 2017 study looked at computer models of amorphous ice, and this let them look at really, really long-range structures, not just close, local ones.

They found that in some amorphous ices, the arrangement of the H2O molecules was just a little bit different than it had been in the liquid water.

They found an internal pattern that can be classified as disordered hyperuniformity.

Liquids have order only over short distances, and crystals have order over long distances, and hyperuniformity is somewhere in the middle, with disorder over short distances and order over long distances.

And this is cool for more than just knowledge's sake, although I do love those things about water.

Understanding hyperuniformity and what materials our hyperuniform could lead to stronger glasses and ceramics or new silicon electronics with interesting properties.

Until recently, amorphous ice was mainly classified into two categories: low-density amorphous ice and high-density amorphous ice- LDA and HDA.

There were also things like eHDA and VHDA, but I promise we'll talk about those in a second.

These low and high-density modifiers are relative to the density of water.

So even though they would absolutely never exist in the same space at the same time, you can imagine that low-density amorphous ice would float in liquid water and high-density amorphous ice would sink in liquid water.

But you know, that won't happen 'cause the liquid water and the ices won't, they're not gonna exist.

Different temperatures and pressures.

They're not in the same place at the same time.

♪ Bringing back the whiteboard ♪ (playful, impish music) Without knocking down... (object banging) Oh my God.

(whiteboard frame clattering) Oh gosh.

Okay.

Ta-da.

LDA was first made in a lab in the 1930s.

They let water vapor slowly accumulate on a smooth surface at low temperatures and found that it was amorphous rather than crystalline.

Even though it doesn't have a crystal structure, it's still not just a totally random configuration of molecules.

Studies have shown that some forms of LDA have tetrahedrally-arranged clusters of water molecules attached by hydrogen bonds.

They may also form some clathrate cages.

Think clusters of molecules that are arranged like a cage that have a space inside of them.

HDA was first discovered in the 1980s.

You can make it in the lab, assuming that you have very fancy equipment that allows you to compress hexagonal ice at very high pressures and very low temperatures.

There are also different types of HDA, including eHDA, or expanded HDA.

You can make this by heating HDA under pressure, causing some of the molecules to move away from each other.

You can also crush down HDA to get things like very-high-density amorphous ice- VHDA.

Chemists didn't get super creative when they were naming these.

Like in LDA, there can be local structures found in HDA but no long-range order.

Now, as usual, with anything regarding water molecules and ice, I am oversimplifying so that this video isn't two hours long.

I've also, as usual, made an unhinged art project to explain it.

This is a graph of what happens to water at different temperatures and pressures.

As you move water through these different temperatures and pressures, you get things like low-density and high-density amorphous ices, but you also get things like ultra-viscous water and supercooled water.

There is a lot going on here.

There's also this chunk of the graph here referred to as a "no man's land", because there's so far no experimental evidence for either crystalline or solid or liquid, glassy, or whatever forms of ice in here.

Nobody knows what's going on over in this little chunk.

Also, if you get out to megabar pressures, water can start to act like a superionic ice, where the hydrogens start to flow around through like an oxygen lattice.

It is weird, and cool, and over that way on the graph.

And as complicated as all of this is, we are still finding new amorphous forms of ice, including one that fits right here into this density gap.

Between low density and high density, we have finally found medium-density amorphous ice.

Medium-density amorphous ice is right around the density of water, right around 1 gram per centimeter cubed.

If you imagine that it were to exist in the same area as liquid water, it would just hang out right in the middle, just kind of float around in the middle there.

And scientists kind of discovered it by accident.

They were interested in looking at small ice crystals, so they put some ice into a big shaker.

Think something like a paint shaker filled with steel balls and chilled to 77 Kelvin.

My freezer only goes down to about 270 Kelvin.

77 Kelvin is really cold, so... Eh, you can still make a cocktail.

More than being just a medium-density curiosity, this ice has some really interesting properties.

For example, if the scientists compressed the medium-density amorphous ice and then heated it to 153 K, it recrystallized into a more common ice crystal structure, but at the same time, it released heat.

So the question is, where did that thermal energy come from?

And it turns out that the ice had stored the mechanical energy from the ball mill and then later released it as heat when it recrystallized.

And that, to me, is fascinating, that it stored mechanical energy and then released it later as thermal energy.

Now, this isn't an efficient method of energy storage, so you're not gonna make an ice battery anytime soon.

But the scientist theorized that it could have implications on icy moons.

Tidal forces there might cause shear forces similar to the ones found in the ball mill.

That means that there could be ice that is storing and releasing energy, leading to ice quakes on some of our solar system's icy moons.

Closer to home, we put low-density amorphous ice to work in science labs, specifically on things like electron microscopy.

If you wanna study the proteins or structures inside of living cells using something like electron microscopy, you have to find a way to fix or freeze them in place before you take a look at them.

If you did this just by freezing it regularly, the water inside those living cells would freeze into large ice crystals and disrupt all of those structures, breaking them apart.

So instead, in cryo-electron microscopy, scientists turn the water inside into amorphous ice.

This basically locks it into the configuration it would've been in as a liquid through jet-freezing, plunge freezing, or vitrification.

These methods discourage large, disruptive crystals and encourage tiny crystals or glassy amorphous ice.

And of course, amorphous ice doesn't just exist in the lab.

Surprisingly, there is some data that suggests it might be found here on Earth, or high above Earth.

The super-duper cold temperatures in our upper atmosphere can cause ice to form in really weird ways.

These include things like hexagonal, cubic, and disordered ice states that we talked about in our last ice crystal video, but it could potentially also include amorphous ice, according to one source that I found.

And then one of our experts was like, "You have a source for this?"

And I was like, "Yeah, there is a source for this, "but we're gonna add some potentials in there."

"But it could potentially also include amorphous ice."

I've already mentioned that it's likely found on icy moons in our solar system, but it's actually, most likely, the most common form of water just out there in space in general.

In addition to moons, it's found on icy dust particles and comets.

And basically, anything that is icy and watery off of Earth's surface, it's gonna be amorphous ice.

And that can tell us something about those objects.

On some icy moons, the presence of crystalline ice indicates a high-temperature region.

Just because they're so cold, that normal crystalline ice means that things must be pretty cozy out there.

But the longer that ice sits on the surface, the more it gets bombarded by ions, and that ion bombardment can change crystalline ice into amorphous ice.

So scientists can look at the fraction of crystalline to amorphous ice to estimate the age of things like geological and tectonic features.

The more crystalline to amorphous ice there is, the younger that region of the planet or moon.

A 2021 study used this to investigate Dione, a moon of Saturn.

The study suggested that Dione might have had tectonic activity within the past hundred million years.

And I know that sounds like a really long time ago but in space terms, that's actually pretty recent.

It also suggested that there might be a liquid ocean underneath the icy crust.

And where you find liquid water, you might find life.

That's hopeful biologist me talking, not the actual scientists.

But like, a girl can dream.

Look, I can't take this board down because we could discover a new form of amorphous or crystalline ice at any moment, and we would have to make a video about it, right?

We couldn't just let a new form of ice go uncovered.

You'd need to let me make a video about it, right?

Please?

Please?

Can I talk more about ice?